IEEE_754 logic

[Thomas Hoffmann]

> >>>>> Peter Dalgaard BSA writes:  
> > > Thomas Hoffmann <hoffmann@ehmgs2.et.tu-dresden.de> writes:  
> >> 3.  The C9x draft introduces
the is*() functionality under the name of "classification MACROS".  If an 
> >>implementation implements this standard, autoconf misses isnan() and isfinite().
> >>

The problem for me is, that if isnan and isfinite are the way C9x says (i.e.
are MACROS), then configure concludes "not there" (AC_FUNCS misses macros
(intentionally)).

>From this it reasons "not IEEE 754".

Then I get back to a native finite() in Arith.h, but IEEE 754 mode was switched
off.

So I see two topics:

1.  Maybe not to (only) check if isnan/isfinite are library functions, but also
to check for working macros (I have not found a predefined macro in Autoconf for
this).

This seems of some importance to me, because it is not only an idiosyncracy of a
singular system, but may become a more widespread problem if systems become C9x
compliant someday.

2.  Introduce a more bulletproof check for IEEE 754.

Is there possibly a computation we can carry out and conclude from its result to
IEEE 754?  I just have no idea.

=============================================================================
Thomas Hoffmann, Institut fuer Halbleiter- und Mikrosystemtechnik, TU Dresden
E-mail:  hoffmann@ehmgs2.et.tu-dresden.de
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